1. Field of the Invention
The present invention relates to an optical disc system, and more particularly, to an apparatus and method for generating a radio frequency (RF) signal and control signals in an optical disc system.
2. Description of the Related Art
As the information age develops, data transmission speed and the volume of information transmitted progressively increase. One method for storing such information is a magnetic method, which is considered a contact method. Another method is an optical method. However, for convenience and mobility of storage media, an optical storing system is favored over a magnetic disc. In a method for implementing an optical storing system, compact discs (CDs) and digital versatile discs (DVDs) have been developed. In a system for storing or restoring data using an optical disc, the amount of light reflected from the surface of a disc is varied by manipulating the surface of the disc and projecting a laser onto the surface of the disc. In an optical disc restoring system, the quantity of light reflected from the disc is converted into an electrical signal. The electrical signal is then restored into an analog signal having the same intensity. In order to sense the quantity of light reflected from the disc, a photodiode is used as a light receiving element, and the amount of current flowing through the photodiode varies according to the amount of light sensed. Depending on the kind of system, four diodes, referred to as A, B, C, and D, to six photodiodes, referred to as A, B, C, D, E, and F, are typically used.
FIG. 1 is a block diagram of a conventional apparatus for generating a radio frequency (RF) signal and control signals in an optical disc system. The apparatus includes a RF summing & automatic gain control (AGC) unit 100, a RF equalizer 110, a data slicer 120, a phase locked loop (PLL) 130, a tracking error detecting unit 140, a focusing error detecting unit 150, a multiplexer 160, an analog/digital converter (ADC) 170, an ERM & error correction code (ECC) decoder 180, and a servo processing unit 190.
References A0, B0, C0, and D0, which are shown in FIG. 1, denote voltage signals determined by converting the current output from each of the four photodiodes A, B, C, and D into voltage signals. The RF summing & AGC 100 sums the four voltage signals A0, B0, C0, and D0 and amplifies the sum of the four voltage signals to generate an analog RF signal. The analog RF signal is asymmetrically corrected by the RF equalizer 110 and the data slicer 120 and is converted into a square waveform signal consisting of logical 1's and/or 0's by comparing the signal with a predetermined reference voltage, thus restoring data. Also, the focusing error detecting unit 150 and the tracking error detecting unit 140 calculate a time difference and a phase difference between the voltage signals A0 and C0 and between the voltage signals B0 and D0 and determined a focusing error (FE) and a tracking error (TE), respectively.
However, as mentioned above, separate analog circuits such as the RF summing & AGC 100, the tracking error detecting unit 140, and the focusing error detecting unit 150 are used to obtain the RF signal, the focusing error (FE), and the tracking error (TE). Due to this use of separate analog circuits, a controlling method of the system can become complicated. Also, since the RF signal is an analog signal, the RF equalizer 110 and the data slicer 120, which are used for signal correction, are implemented by analog circuits. In the case of using analog circuits, errors can occur during data restoration due to deviations caused by analog elements. Thus, the reliability of the entire system deteriorates. Also, since many analog elements are used, it is difficult to implement an optical disc system with one chip.